Applied following patches from Robert Collins and make sure IN_LIBXML is

* libxml.h: Applied following patches from Robert Collins
  and make sure IN_LIBXML is defined when compiling it
-------
* include/libxml/xmlversion.h.in (LIBXML_DLL_IMPORT): Use on Cygwin
  as well as Visual C.
* parser.c (XML_DIR_SEP): Don't use '\\' for Cygwin.
* parserInternals.c (XML_DIR_SEP): Don't use '\\' for Cygwin.
* strio.c (PLATFORM_UNIX): Define for Cygwin.
* triodef.h (TRIO_PLATFORM_UNIX): Define for Cygwin.
* xmlIO.c (xmlFileOpen): Use unix behaviour for Cygwin.
  Use binary mode opens for Cygwin (xmlFileOpenW xmlParserGetDirectory
  xmlSysIDExists xmlNoNetExists).
* xmllint.c: Don't include winsock2.h for Cygwin.
Daniel
diff --git a/triodef.h b/triodef.h
index 407ea03..a3ca8b6 100644
--- a/triodef.h
+++ b/triodef.h
@@ -48,6 +48,8 @@
 # define TRIO_PLATFORM_UNIX
 #elif defined(__QNX__)
 # define TRIO_PLATFORM_UNIX
+#elif defined(__CYGWIN__)
+# define TRIO_PLATFORM_UNIX
 #elif defined(AMIGA) && defined(TRIO_COMPILER_GCC)
 # define TRIO_PLATFORM_UNIX
 #elif defined(TRIO_COMPILER_MSVC) || defined(WIN32) || defined(_WIN32)